Method of Determining a Temperature of a Transistor, Transistor Driver Device and System

This application claims priority to Germany Patent Application No. 102024114320.7 filed on May 22, 2024, the content of which is incorporated by reference herein in its entirety.

The present application relates to methods of determining a temperature of a transistor, a transistor driver device capable of determining the temperature of a transistor and a system including such a driver device.

In various circumstances, it may be desirable to measure or estimate the temperature of a transistor, for example the so-called junction temperature, e.g., the temperature of a chip including the transistor, for example inside a package. Providing a temperature sensor on the package may lead to delays and imprecisions in the measured temperature, as the temperature measured may not correctly reflect the temperature of the transistor itself.

One example of an application where measuring the temperature is desirable is overtemperature protection of transistors, e.g., detecting if the temperature of the transistor becomes too high and then introducing countermeasures like turning the transistor off. Other applications may include temperature dependent calibrations.

According to an implementation, a method of determining a temperature of a transistor is provided, including: providing a current pulse of predefined length and predefined current magnitude to a control terminal of a transistor, measuring a voltage at the control terminal, and determining the temperature of the transistor based on the measured voltage.

In another implementation, a transistor driver device is provided, including: a driver circuit configured to provide a current pulse of predefined length and predefined current magnitude at a driver output terminal, a voltage measurement device configured to measure a voltage at the driver output terminal, and an evaluation device configured to determine a temperature of a transistor based on the measured voltage.

A system including such a transistor driver device and the transistor is also provided, where the driver output terminal is coupled to a control terminal of the transistor.

The above summary merely gives a brief overview over some implementations and is not to be construed as limiting, as other implementations may include different features than the one described above.

In the following, various implementations will be described in detail referring to the attached drawings. These implementations are provided as examples only and are not to be construed as limiting.

Details, variations and modifications described with respect to one of the implementations may also be applied to other implementations and are therefore not to be construed as limiting.

is a block diagram of a system according to an implementation, including a transistor driver deviceaccording to an implementation and a transistor. Generically, a transistor as used herein is described as including a control terminaland two load terminals,. As example, in some of the following implementations insulated gate bipolar transistors (IGBTs) where control terminalis a gate terminal and the first and second load terminal,are an emitter terminal and a collector terminal, respectively, are used. However, implementations are not limited to IGBTs, and for example field effect transistors, where control terminalcorresponds to a gate terminal, load terminalcorresponds to a source terminal and load terminalcorresponds to a drain terminal may also be used.

Transistor driver deviceincludes a driver circuit. Driver circuitin the implementation ofis a current source based driver, as explained later in more detail with respect to, which delivers a current to control terminalto charge or discharge control terminalwith respect to load terminal, to establish a corresponding gate-source or gate-emitter voltage to control transistor. A current source based driver circuit means that a current source is used to deliver a predefined or controlled gate current, instead of using a voltage source together with a gate resistor in a voltage source based driver.

While for simplicity driver circuitis shown as only connected to the control terminalvia a driver output terminal, as will be shown below, the driver circuit may be additionally connected to load terminalor an auxiliary load terminal as a return path and reference.

Driver circuitmay be operated to turn transistoron and off, essentially as in conventional driver circuits, by charging or discharging control terminal.

Furthermore, for measuring a temperature of transistor, driver circuitmay be configured to provide a current pulse of a predefined duration and current to control terminal. The duration and current may be independent from the type of transistor used, whereas for example otherwise a current for turning transistoron or off may be dependent on the type of transistor. This current pulse will be also referred to as first current pulse hereinafter.

It should be noted that providing a current may include providing a positive current for charging control terminalor a negative current for discharging control terminal. Depending on transistor type, one of the charging or discharging may turn transistoron, and the other one of charging or discharging may turn transistoroff. In some of the following examples, it will be assumed that charging control terminal, e.g., providing a current from driver circuitto control terminal, turns transistoron, and discharging control terminal, e.g., providing a current from control terminalto driver circuit, turns transistoroff.

As will be explained below in more detail, the first current pulse may be part of a turning on of transistor, part of a turning off of transistor, or may be provided outside a switching operation of transistor. The first current pulse may transfer a charge amount to or from control terminalwhich alone is not sufficient to switch transistorbetween its on and off state. For switching transistor, the first current pulse may be combined with a second current pulse, which may for example be longer than the current pulse, and/or have a different current magnitude, and may be adapted to the type of transistor, and in combination with the first current pulse may provide sufficient charge transfer for switching the transistor.

Transistor driver deviceadditionally comprises a voltage measurement device. Voltage measurement deviceis configured to measure a voltage at the driver output terminal. The measured voltage approximately corresponds to a voltage at control terminalbecause in operation of the system control terminalis coupled to driver output terminalwith a low ohmic connection. In other implementations, a separate measurement input of transistor driver devicecoupled to control terminalmay be used. In some implementations, a voltage measurement device may be provided directly at control terminal, and the measured voltage may be provided to an evaluation deviceexplained further below. In some cases, this may increase accuracy by avoiding effects of the connection between driver output terminaland control terminal, but requires the voltage measurement device to be provided directly at control terminal. In the following, the term “measuring the voltage at control terminal” will be used, with the understanding that this voltage may be measured entirely in driver deviceby voltage measurement circuitcoupled to driver output terminalas shown.

Measuring a voltage at control terminalis to be understood as measuring the potential difference between control terminaland a reference potential. In some implementations, the reference potential is a voltage at load terminal, for example source voltage for a field effect transistor or emitter voltage for an IGBT. In some implementations, transistormay include an auxiliary load terminal, for example auxiliary emitter terminal or auxiliary source terminal, coupled to transistor driver deviceand providing a return path for the current provided to control terminal. In this case, the reference voltage may be a voltage at such an auxiliary load terminal, as measured in transistor driver deviceusing voltage measurement circuit. In yet other implementations, the reference voltage may be a fixed reference voltage like ground.

To measure the temperature of transistor, the voltage at control terminalis measured concurrently with applying the first current pulse. Based on the measured voltage, then evaluation devicedetermines the temperature. In particular, in this way for example a peak voltage at control terminalwhile applying the first current pulse may be determined, and the temperature may be determined based on this peak voltage. For example, evaluation devicemay determine the temperature based on calibration data like a calibration curve or a lookup table, which translates the measured voltage to a temperature. For such a calibration procedure, the temperature of transistormay be measured by other means, for example by a temperature sensor thermally coupled to transistorand/or incorporated in transistorfor calibration purposes.

While driver circuit, voltage measurement deviceand evaluation deviceare shown as separate blocks in, two or more may be integrated in a common circuit on a common chip. In other implementations, several chips may be used. In yet other implementations, evaluation devicemay be provided remotely and receives the voltage measurement data from voltage measurement devicevia some communication connection like a wire based connection or a wireless connection. The evaluation device may be implemented in hardware and/or software. In a hardware implementation, the evaluation device can be embodied, for example, as a computer or as a microprocessor. Thus, the evaluation device may include one or more processors. In a software implementation, the evaluation device can be embodied as a computer program product, as a function, as a routine, as an algorithm, as part of a program code or as an executable object.

is a flow chart illustrating a method according to an implementation, which may be implemented in the system of, but is not limited thereto. Nevertheless, to avoid repetitions, the method ofwill be explained referring to.

At, the method comprises providing a first current pulse to a control terminal of a transistor, for example by driver circuitofas explained above. At, the method comprises measuring a voltage at the control terminal of the transistor concurrently with applying the first current pulse, as explained with respect to voltage measurement deviceof. At, the method comprises determining the temperature of the transistor based on the measured voltage.

To explain further,shows a simplified equivalent circuit of a current source driver as used in an some implementations.illustrates a schematic view of a corresponding transistor.

As an example, an insulated gate bipolar transistor (IGBT)is used in, which may be implemented as an IGBT chipmounted to a base, including for example a DBC (direct bonded copper) plate, which in turn is provided on a base plate. A collector terminalof IGBT chipmay be directly provided on DBC plate, and a gate terminaland an emitter terminalmay be coupled using bond wires,.

IGBTis illustrated as an equivalent circuit with a core IGBT, which represents an ideal IGBT without parasitics, a collector-emitter capacitance C, a gate-collector capacitance C, a gate-emitter capacitance C, and an internal resistance Rbetween a gate terminalof IGBTand a gate nodeof core IGBT. This internal resistance Rin practical cases dominates the overall resistance between a driver, represented by a current source, and internal gate node, such that the resistance e.g., caused by a bond wire like bond wirecoupling the driver to gate terminalmay be neglected in the discussions below.

Returning to, a current sourceprovides a gate current Ito a gate terminalof IGBT, which may be gate padof IGBT chipof. As mentioned above, the gate current Imay be positive or negative. In other implementations, a field effect transistor like a MOSFET may be used.

The gate current IG is provided to internal gate nodevia an inductance LG, which may for example predominantly include an inductivity of a bond wire used, like bond wire, and may also include an inductivity of other circuit paths, and internal resistance Rint between gate terminaland internal gate node, which as explained above dominates the resistance between driver (e.g., current source) and internal gate node. For example, IGBTmay include trench gate structures that are connected to the gate pad (e.g.,) via a gate runner and internal resistance Rint, for example. We note that internal resistance Rint may be caused by a different structure and/or material than the gate pad, the gate runner and/or the gate structure, such as gate trenches.

A voltage between collector and emitter of core IGBTis labelled V, a current flowing from the emitter terminal is labelled I, and an inductance of a connection to the source terminal, which offers a return path for current source, is labelled L. For switching transistor, inter alia the gate emitter capacitance Cis charged or discharged by gate current I.

The internal resistance Ris temperature dependent. For example, in an operating range the dependency may be essentially linear, as shown by a curveof, which shows the internal resistance Rover the junction temperature T. Other dependencies may also exist depending on transistor implementation.

In good approximation, the internal resistance Rmultiplied with the gate current Icorresponds to a voltage Vdrv across the current source. This voltage in turn, for a given reference potential at the emitter terminal, corresponds to the voltage at gate terminalin, which essentially corresponds to measuring the voltage at driver output terminalshown in, as Ris internal to IGBTand a resistance of a connection to the driver like a resistance of bond wiremay be neglected in comparison. The inductance Lis mainly caused by the electrical connection, for example bond wire, between the transistor driver deviceand the transistor like transistor. This is unlike the situation in voltage source based drivers, where an external gate resistor must be provided which dominates the resistance between driver and transistor, in contrast to the present case of a current source driver where the internal resistance dominates.

When the current pulse is predefined, therefore from the above relationship between voltage, current and internal resistance the internal resistance Rmay be determined. Rin turn has a clear relation to the junction temperature, as shown in. By using a current pulse of predefined current magnitude and length and measuring the voltage, the temperature may be determined.

If the voltage at gate terminalis V1 and the voltage at internal gate nodeis V2, then R=(V1−V2)/I. Furthermore, the gate current charges the gate-emitter capacitance Cthus building up V2, according to V2=(I×t)/C, where t is the duration of the gate current. Combining the two equations leads to R=V1/I−t/C.

This means that for a certain transistor having a certain fixed C, when the above-mentioned first predefined current pulse of predefined current magnitude, e.g., predefined I, and predefined duration, e.g., predefined t, is applied, V2 is fixed by this pulse, and variations of V1 depend only on variations of R. Therefore, by measuring V1, e.g., the voltage at gate terminal, a measure of Rand thus of the temperature Tj (see) may be obtained.

illustrates an example of using the above mentioned first current pulse of predefined current magnitude and predefined length together with a second current pulse during turning on of a transistor. A curveinshows the gate current during a turn on procedure, and a curveillustrates the gate emitter voltage. At a time tand to a time t, a first current pulseis applied with a current level Iand a duration from tto t. This first current pulse may have a duration of 100 to 150 nanoseconds, but is not limited thereto. At the end of the first current pulse, the gate emitter voltage of curveis still below the threshold voltage V, such that the first current pulsedoes not turn the transistor on.

After the first current pulse, a second current pulseis applied, which has a lower current Iand a longer duration, essentially from tto t, than the first current pulse. Within a short time after t, the gate emitter voltage reaches the threshold voltage Vand then the Miller plateau voltage V. After t, the voltage then rises to the full voltage V, and the gate current according to curvedecreases to zero, meaning that the gate is fully charged.

shows simulation results for a situation as shown inturning on an IGBT. A curveshows the collector emitter current of the transistor, a curveshows the gate current (similar to curveof), a curveshows the collector emitter voltage, and curves,show the gate emitter voltage.

The gate current includes a first current pulse, as explained referring tofor first current pulse. In response to current pulse, the gate emitter voltage also exhibits a peak. Curveshows the case for a junction temperature of 150° C., and curveillustrates the case for a junction temperature of 25° C. As can be seen, the voltages differ and therefore may serve as a measure for the junction temperature. For measurement, for example the maximum gate emitter voltage during first current pulse, or a gate emitter voltage at the end of first current pulse, an average gate emitter voltage during first current pulseor another clearly defined voltage may be used.

It should be noted that while single curvesandfor collector-emitter current and collector-emitter-voltage are shown, these curves may vary slightly with temperature, which, however, does not affect the temperature measurement discussed herein and has therefore been omitted fromand the following Figures.

During the first predefined current pulse, the transistor as explained above is below its threshold, e.g., not turned on, and no load current flows. Measurement with different current magnitudes in the second current pulse for different turn-on speeds show that the voltage Vge measured concurrently with the first predefined current pulse are independent of such different second current pulses. They are also independent from the load current flowing after the transistor is turned on.

As mentioned above, the relationship between this voltage thus measured and the junction temperature may be obtained via calibration.

In the examples of, the current pulse occurs at the start of a turning on of the transistor. This is not limiting, and further possibilities will now be explained referring to.show curves for the same quantities as, namely the collector emitter current Ice, the gate current Ig, the collector emitter voltage Vce, and the gate emitter voltage V, e.g., the voltage measured for example by voltage measurement deviceof.

In, a curveshows the collector emitter current, a curveshows the gate current, a curveshows the collector emitter voltage. The gate emitter voltage is shown for two different temperatures. In the example of, a first current pulseis provided at the end of the gate current flowing for turning on the transistor, e.g., after the corresponding second current pulse. A curveillustrates a case for a temperature of 150° C. junction temperature, and curveshows a case for a junction temperature of 25° C. Therefore, also here by measuring the voltage during the current pulse, the junction temperature may be determined. Similar to, for measurement, for example the maximum gate emitter voltage during first current pulse, or a gate emitter voltage at the end of first current pulse, an average gate emitter voltage during first current pulseor another clearly defined voltage may be used.

shows a further example for a turn on, and a curveshows the collector emitter current, a curveshows the gate current, a curveshows the collector emitter voltage and curves,show the gate emitter voltage for two different temperatures. In, a first current pulseis provided approximately in the middle of the turning on, e.g., in the middle of the second current pulse. Curveshows the response for a junction temperature of 150° C., and curveshows the response, e.g., the gate emitter voltage, or a junction temperature of 25° C. Also here, by measuring the voltage concurrently with the current pulse, the temperature may therefore by determined. Similar to, for measurement, for example the maximum gate emitter voltage during first current pulse, or a gate emitter voltage at the end of first current pulse, an average gate emitter voltage during first current pulseor another clearly defined voltage may be used.

show examples for applying a first current pulse in the course of turning on the transistor. Next, examples for applying the current pulse in the course of turning off the transistor will be explained referring to. A curveillustrates the collector emitter current, a curvethe gate current, a curvethe collector emitter voltage, and curves,the gate emitter voltage. In this case, a first current pulseand the second current pulse provide a negative current for discharging the gate, such that the transistor is turned off, the collector emitter voltage rises to the corresponding blocking voltage and the collector emitter current decreases. In the example of, similar to, the current pulseis at the start of the turning off.

Curveshows the response for a junction temperature of 150° C., and curveshows the response for 25° C. junction temperature. As can be seen, also here a clear dependency of the gate emitter voltage from the temperature exists, and by measuring the voltage the junction temperature may be determined. Similar to, for measurement, for example the maximum gate emitter voltage during first current pulse, or a gate emitter voltage at the end of first current pulse, an average gate emitter voltage during first current pulseor another clearly defined voltage may be used.

In, a curveshows the collector emitter current, a curveshows the gate current, a curveshows the collector emitter voltage and curves,show the gate emitter voltage. In this case, the first current pulse, again with a negative current for turning off the transistor, is provided at the end of the turning off, e.g., after the second current pulse. Curveshows the gate emitter voltage for a junction temperature of 150° C., and curveshows the gate emitter voltage for a junction temperature of 25° C. Also here, measuring the voltage allows determining of the junction temperature. Similar to, for measurement, for example the maximum gate emitter voltage during first current pulse, or a gate emitter voltage at the end of first current pulse, an average gate emitter voltage during first current pulseor another clearly defined voltage may be used.

In, a curveshows the collector emitter current, a curveshows the gate current, a curveshows the collector emitter voltage, and curves,show the gate emitter voltage. Here, the first current pulseis provided approximately in the middle of the second current pulse, or, in other words, approximately in the middle of the turn off procedure (similar to, where the first current pulse was provided approximately in the middle of the turning on of the transistor). Curveshows a gate emitter voltage for a junction temperature of 150° C., and curveshows the gate emitter voltage for a junction temperature of 25° C. Also here, by measuring the voltage the temperature may be determined.

shows a further example where the first current pulse takes place while the transistor is turned off, e.g., outside a switching event of the transistor. In, a curveshows the collector emitter current, a curveshows the gate current, a curveshows the collector emitter current, and curvesshow the gate emitter voltage. In the example of, the first current pulse includes a first sub-pulseand a second sub-pulse.

In the example of, the first and second sub-pulses,have the same duration, e.g., around 60 ns, and same current magnitudes, but with opposite signs. The first sub-pulsehas a positive current thus charging the gate, and the second sub-pulsehas a negative current, thus discharging the gate. As duration and current magnitude are equal, after the first and second sub-pulses,the gate charge essentially is the same as before the first and second sub-pulses,. It should be noted that in other implementations the duration and current magnitude may not be the same, and still the charge may be preserved, as long as the integral of current over time for the first sub-pulse is minus the integral of current over time for the second sub-pulse, e.g., the same amount of charged is transferred by both sub-pulses,. As a simple example, in another implementation second sub-pulsemay have a duration twice the duration of the first sub-pulse, but half the current magnitude. Same amount of charge or equal charge may mean equal or the same within some tolerance, e.g., 10%.